Abstract

A guide wire (1) has a wire body (10) having a
first wire (2) disposed at a distal end thereof and a
second wire (3) joined to a proximal end of the first
wire. The first wire (2) and the second wire (3) are
preferably joined to each other by welding, providing a
layer joint (14) therebetween. The joint (14) is of a
curved shape, particularly, a convex curved shape that is
convex toward the proximal end of the wire body (10). In
the joint (14), at least one component (e.g., Ti) of the
material of the first wire (2) decreases toward the
proximal end, and at least one component (e.g., Fe) of
the material of the second wire (3) decreases toward the
distal end. When a tensile test is conducted on a region
of the wire body (10) including the joint (14), the
region of the wire body (10) has, in a tensile load and
elongation diagram, an elastic section extending
substantially straight upwardly to the right, a yield
section extending substantially horizontally or upwardly
to the right from the elastic section, and a
substantially straight section extending upwardly to the
right from the yield section. The region of the wire
body (10) has such characteristics that the region is
fracturable near a terminal end of the straight section
at a fracture position on other than the joint (14).

Description

BACKGROUND OF THE INVENTIONField of the Invention:

The present invention relates to a guide wire, and
more particularly to a guide wire for use in introducing
a catheter into a body cavity such as a blood vessel.

Description of the Related Art:

Guide wires are used to guide a catheter for
treating a body region that a surgical operation such as
PTCA (Percutaneous Transluminal Coronary Angioplasty)
cannot be performed on, treating a human body on a
minimally invasive basis, or diagnosing a cardiovascular
according to angiography. A guide wire used in PTCA is
combined with a balloon catheter such that the distal end
of the guide wire projects from the distal end of the
balloon catheter, and is inserted together with the
balloon catheter into a position near a constricted area
of a blood vessel. Then, the guide wire guides the
distal end of the balloon catheter to the stenosis area
of the blood vessel.

Blood vessels are of intricately curved shape.
Guide wires used to insert balloon catheters into such
blood vessels are required to have flexibility and
elasticity upon bending, pushability and torque
transmission performance for transmitting a control
action on the proximal end toward the distal end (these
features will collectively referred to as "steerability"),
and kink resistance (fold resistance). Guide wire
structures for achieving flexibility among the above
features include a structure in which a metal coil having
flexibility upon bending is wound around a core at the
slender distal end of a guide wire and a structure in
which a superelastic wire of Ni-Ti or the like is used as
a guide wire core for giving flexibility and elasticity.

Conventional guide wires have a core made
essentially of one material. For increased steerability
of guide wires, the core is made of a material having a
relatively high modulus of elasticity, which tends to
make the distal end of the guide wire less flexible. If
the core is made of a material having a relatively low
modulus of elasticity for making the distal end of the
guide wire more flexible, then the proximal end of the
guide wire loses its steerability. It has been difficult
to achieve both flexibility and steerability with one
core material.

In order to improve the above shortcomings, U.S.
patent No. 5,171,383, for example, discloses a guide wire
having a core in the form of an Ni-Ti alloy wire and
having distal and proximal ends heat-treated under
different conditions for making the distal end more
flexible and the proximal end more rigid.

However, there are limitations on attempts to
control the flexibility through heat treatment in that
though the distal end may gain sufficient flexibility,
the proximal end may not necessarily be made
satisfactorily rigid.

U.S. patent No. 6,001,068 reveals a guide wire
including a flexible first wire disposed at a distal end
thereof, a highly rigid second wire disposed at a
proximal end thereof, and a tubular connector
interconnecting the first wire and the second wire and
having grooves or slits, the connector being
progressively more rigid from the distal end toward the
proximal end.

The revealed guide wire has wires having desired
characteristics at the respective distal and proximal
ends. Since these wires are interconnected by the
tubular connector, the bonding strength of the wires is
not high, and the wire guide fails to have a sufficient
torque transmission capability. Another problem is that
it is tedious and time-consuming to connect the wires in
the manufacturing process.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide
a guide wire which has sufficient flexibility and
steerability and allows a first wire and a second wire to
be interconnected with high bonding strength.

The above object can be achieved by a guide wire
including a wire body having a first wire disposed at a
distal end thereof and a second wire joined to a proximal
end of the first wire through a joint and made of a
material having an elastic constant greater than the
material of the first wire, wherein the joint between the
first wire and the second wire has a curved shape which
is symmetric with respect to the central axis of the wire
body.

The joint is preferably convex toward the proximal
end of the wire body. The first wire and the second wire
are preferably joined to each other by welding. The
joint preferably includes a layer. The joint in the form
of a layer preferably has a thickness ranging from 0.001
to 100 µm. The wire body preferably has an outside
diameter at the joint which is greater than the outside
diameter of a region of the wire body on a proximal side
of the joint. The wire body preferably has an outside
diameter at the joint which is greater than the outside
diameters of regions of the wire body on proximal and
distal sides of the joint. The guide wire preferably has
a covering layer disposed on an outer circumferential
surface of the wire body in covering relation to at least
the joint. The covering layer is preferably made of a
material capable of reducing friction, such as
thermoplastic elastomer, silicone resin, or fluorine-based
resin. The covering layer preferably has an
average thickness in the range from 1 to 30 µm. The wire
body preferably has a tapered portion whose outside
diameter is progressively reduced toward the distal end.
The guide wire preferably has a helical coil disposed
around at least a distal end portion of the first wire.
Preferably, the materials of the first wire and the
second wire contain a common metal element. The first
wire is preferably made of a superelastic alloy. The
second wire is preferably made of stainless steel or a Co
base alloy. The Co base alloy is preferably a Co-Ni-Cr
base alloy.

The above object can also be achieved by a guide
wire including a wire body having a first wire disposed
at a distal end thereof and a second wire joined to a
proximal end of the first wire through a joint and made
of a material different from the material of the first
wire, wherein in the joint a first component of the
material of the first wire decreases toward the proximal
end and a second component of the material of the second
wire decreases toward the distal end.

The material of the second wire preferably has an
elastic constant greater than the material of the first
wire. The materials of the first wire and the second
wire preferably contain a common metal element. The
first wire is preferably made of an Ni-Ti base alloy.
The second wire is preferably made of stainless steel or
a Co base alloy. The Co base alloy is preferably a Co-Ni-Cr
base alloy. The joint is preferably of a curved
shape, and of a shape which is symmetric with respect to
the central axis of the wire body. The joint is
preferably convex toward the proximal end of the wire
body. The first wire and the second wire are preferably
joined to each other by welding. The joint in the form
of a layer preferably has a thickness ranging from 0.001
to 100 µm. The wire body preferably has an outside
diameter at the joint which is greater than the outside
diameters of regions of the wire body on proximal and
distal sides of the joint. The guide wire preferably has
a covering layer disposed on an outer circumferential
surface of the wire body in covering relation to at least
the joint. The covering layer is preferably made of a
material capable of reducing friction, such as
thermoplastic elastomer, silicone resin, or fluorine-based
resin. The covering layer preferably has an
average thickness in the range from 1 to 30 µm. The wire
body preferably has a tapered portion whose outside
diameter is progressively reduced toward the distal end.
The guide wire preferably has a helical coil disposed
around at least a distal end portion of the first wire.
In the joint, the first component and/or the second
component preferably has a plurality of different
concentration gradients in the longitudinal direction of
the wire body. The different concentration gradients
include a first concentration gradient and a second
concentration gradient which are relatively gradual, and
a third concentration gradient positioned between the
first concentration gradient and the second concentration
gradient and steeper than the first concentration
gradient and the second concentration gradient.

The above object can further be achieved by a guide
wire including a wire body having a first wire disposed
at a distal end thereof and made of a pseudoelastic
material, and a second wire joined to a proximal end of
the first wire through a joint by welding and made of a
material having an elastic constant greater than the
material of the first wire, wherein a region of the wire
body including the joint has, in a tensile load and
elongation diagram, an elastic section extending
substantially straight upwardly to the right and a yield
section extending substantially horizontally or upwardly
to the right from the elastic section, the region of the
wire body having such characteristics that the region is
fracturable at a fracture position under a load higher
than a terminal end of the yield section, the fracture
position being on other than the joint.

The above object can also be achieved by a guide
wire including a wire body having a first wire disposed
at a distal end thereof and made of a pseudoelastic
material, and a second wire joined to a proximal end of
the first wire through a joint by welding and made of a
material having an elastic constant greater than the
material of the first wire, wherein when a tensile test
is conducted on a region of the wire body including the
joint, the region of the wire body has, in a tensile load
and elongation diagram, an elastic section extending
substantially straight upwardly to the right, a yield
section extending substantially horizontally or upwardly
to the right from the elastic section, and a
substantially straight section extending upwardly to the
right from the yield section, the region of the wire body
having such characteristics that the region is
fracturable near a terminal end of the straight section,
the joint having a higher fracture strength than the
distal end of the second wire.

The above object can further be achieved by a guide
wire including a wire body having a first wire disposed
at a distal end thereof and made of a pseudoelastic
material, a second wire made of a material having an
elastic constant greater than the material of the first
wire, and a joint produced by joining a proximal end of
the first wire and a distal end of the second wire to
each other by welding, the joint having a higher fracture
strength than the distal end of the second wire.

The tensile load and elongation diagram preferably
includes a tensile load and elongation curve which is
curved downwardly due to necking of the guide wire when
the guide wire is going to be fractured. The wire body
preferably has a fracture strength of at least 4 kgf (445
MPa). The first wire is preferably made of a
superelastic alloy. The second wire is preferably made
of stainless steel or a Co base alloy. The joint between
the first wire and the second wire is preferably of a
curved shape which is symmetric with respect to the
central axis of the wire body. The joint is preferably
convex toward the proximal end of the wire body. The
joint preferably includes a layer. The joint in the form
of a layer preferably has a thickness ranging from 0.001
to 100 µm. The covering layer is preferably made of a
material capable of reducing friction, such as
thermoplastic elastomer, silicone resin, or fluorine-based
resin. The covering layer preferably has an
average thickness in the range from 1 to 30 µm. The wire
body preferably has a tapered portion whose outside
diameter is progressively reduced toward the distal end.
The guide wire preferably has a helical coil disposed
around at least a distal end portion of the first wire.
Preferably, the materials of the first wire and the
second wire contain a common metal element.

The above object can further be achieved by a
guide wire comprising a wire body having a first wire
disposed at a distal end thereof and a second wire joined
to a proximal end of the first wire through a weld joint
and made of a material different from the material of the
first wire, the materials of the first wire and the
second wire contain a common metal element, the first
wire is made of a Ni-Ti base alloy, the weld joint
including at least a portion such that at least one
component of the material of the first wire decreases
toward the proximal end, and at least a portion such that
at least one component of the material of the second wire
decreases toward the distal end.

The above object can further be achieved by a
guide wire comprising a wire body having a first wire
disposed at a distal end thereof and a second wire joined
to a proximal end of the first wire through a weld joint
and made of a material different from the material of the
first wire, the materials of the first wire and the
second wire contain a common metal element, the first
wire is made of a Ni-Ti base alloy, the weld joint
including at least a portion such that at least one
component of the material of the first wire decreases
toward the proximal end.

The above object can further be achieved by a guide
wire comprising a wire body having a first wire disposed
at a distal end thereof and a second wire joined to a
proximal end of the first wire through a weld joint and
made of a material different from the material of the
first wire, the materials of the first wire and the
second wire contain a common metal element, the first
wire is made of a Ni-Ti base alloy, the weld joint
including at least a portion such that at least one
component of the material of the second wire decreases
toward the distal end.

According to the present invention, the guide wire
has a high bonding strength between the first wire and
the second wire. Since the first wire and the second
wire which have different physical characteristics are
joined to each other, the guide wire has sufficient
flexibility and steerability. Even when stresses such as
bending or tensile stresses are applied to the guide wire,
the joint between the first wire and the second wire is
prevented from being broken. The guide wire is capable
of reliably transmitting torsional torques or pushing
forces from the proximal end to the distal end.

The above and other objects, features, and
advantages of the present invention will become apparent
from the following description when taken in conjunction
with the accompanying drawings which illustrate a
preferred embodiment of the present invention by way of
example.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a longitudinal cross-sectional view of a
guide wire according to an embodiment of the present
invention;

Fig. 2 is an enlarged fragmentary longitudinal
cross-sectional view of a joined region of a wire body of
the guide wire shown in Fig. 1;

Fig. 3 is a graph showing the results of an Auger
electron spectroscopic analysis of the longitudinal
composition of the wire body of the guide wire shown in
Fig. 1;

Fig. 4 is a diagram showing the relationship
between tensile loads and elongations in a tensile test
conducted on the wire body shown in Fig. 1;

Figs. 5(a) and 5(b) are diagrams each showing the
relationship between tensile loads and elongations in
tensile tests conducted on the wire body shown in Fig. 1;

Fig. 6 is a diagram showing the relationship
between tensile loads and elongations in a tensile test
conducted on the wire body shown in Fig. 1;

Fig. 7 is a view illustrative of an example in
which the guide wire shown in Fig. 1 is used; and

Fig. 8 is an enlarged view illustrative of the
example in which the guide wire shown in Fig. 1 is used.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Fig. 1 shows in longitudinal cross section a guide
wire according to an embodiment of the present invention,
and Fig. 2 shows in enlarged fragmentary longitudinal
cross section a joined region of a wire body of the guide
wire shown in Fig. 1.

In Fig. 1, the guide wire is illustrated as being
contracted in the longitudinal direction and as being
enlarged or exaggerated in the transverse direction for
an easier understanding of the invention. Therefore, the
ratio of illustrated dimensions in the longitudinal and
transverse directions is different from the ratio of
actual dimensions.

The guide wire, generally denoted by 1 in Fig. 1,
is a guide wire to be inserted in a catheter, and
includes a wire body 10 having a first wire 2 disposed at
a distal end thereof and a second wire 3 disposed at a
proximal end thereof and joined to the first wire 2, and
a helical coil 4 combined with the wire body 10. The
guide wire 1 has an overall length which is preferably in
the range from 200 to 5,000 mm. The guide wire 1 has an
outside diameter, i.e., an outside diameter over a
constant-outside-diameter portion thereof, which is
preferably in the range from 0.2 to 1.4 mm.

The first wire 2 is made of an elastic wire
material and has a length which is preferably in the
range from 20 to 1,000 mm.

According to the present embodiment, the first wire
2 has a portion having a constant outside diameter and a
portion (tapered portion) having an outside diameter
progressively smaller toward the distal end. The first
wire 2 may have one or two or more tapered portions. In
the illustrated embodiment, the first wire 2 has two
tapered portions 15 and 16.

The first wire 2 with the two tapered portions 15,
16 has its rigidities (flexural rigidity and torsional
rigidity) gradually reduced toward the distal end. As a
result, the guide wire 1 is flexible enough at a distal
end portion for a higher ability to follow curved blood
vessels, better safety, and greater resistance to forces
tending to kink the guide wire 1.

In the illustrated embodiment, the tapered portions
15, 16 are disposed in longitudinally spaced locations on
the first wire 2. However, the first wire 2 may be
tapered in its entirety toward the distal end. The
tapered portions 15, 16 may be tapered at an angle
(diameter reduction ratio) which is constant in the
longitudinal direction or at angles (diameter reduction
ratios) which are different in the longitudinal direction.
For example, the tapered portions 15, 16 may be tapered
at an alternate pattern of relatively large angles
(diameter reduction ratios) and relatively small angles
(diameter reduction ratios).

Unlike the illustrated embodiment, the tapered
portion 16 may have a proximal end positioned somewhere
on the second wire 3, e.g., the tapered portion 16 may be
positioned across a joined (welded) area 14 between the
first wire 2 and the second wire 3.

The first wire 2 may be made of any material, e.g.,
any of various metal materials such as stainless steel.
Particularly, the first wire 2 is preferably made of a
pseudoelastic alloy (including a superelastic alloy), and
more preferably made of a superelastic alloy.
Superelastic alloys are relatively flexible, elastic, and
less plastically deformable. Therefore, if the first
wire 2 is made of a superelastic alloy, then the guide
wire 1 is sufficiently flexible and elastic upon bending
at its distal end portion, and has a better ability to
follow blood vessels that are curved and bent intricately,
so that the guide wire 1 has higher steerability. In
addition, even when the second wire 2 is repeatedly
curved or bent, since the first wire 2 is less
plastically deformable due to its elasticity, any
reduction in the steerability of the guide wire 1, which
would otherwise be caused if the first wire 2 were more
plastically deformable, is avoided.

Pseudoelastic alloys include all pseudoelastic
alloys which exhibit any tensile stress and strain curves,
all pseudoelastic alloys which have transformation
temperatures such as As, Af, Ms, Mf, etc. that can or
cannot be measured distinctly, and all pseudoelastic
alloys which are greatly deformed (strained) under
stresses and recover the original shape upon removal of
stresses.

Preferred compositions of superelastic alloys
include an Ni-Ti base alloy such as an Ni-Ti alloy having
49 to 52 at% of Ni, a Cu-Zn alloy having 38.5 to 41.5 wt%
of Zn, a Cu-Zn-X alloy (X represents at least one of Be,
Si, Sn, A1, and Ga) having 1 to 10 wt% of X, and an Ni-Al
alloy having 36 to 38 at%. Particularly preferable of
these alloys is the Ni-Ti base alloy. The superelastic
alloys typified by the Ni-Ti base alloy are excellent in
its adhesion to a covering layer 5 to be described later.

The second wire 3 has a distal end connected
(joined) to the proximal end of the first wire 2 by
welding, for example. The second wire 3 is made of an
elastic wire material and has a length which is
preferably in the range from 20 to 4,800 mm.

The second wire 3 is preferably made of a material
having elastic constants (Young's modulus (tensile
modulus), modulus of rigidity (shear modulus), and bulk
modulus) which are different from the first wire 2.
Particularly, the second wire 3 is preferably made of a
material having elastic constants which are greater than
the first wire 2. The second wire 3 made of such a
material has appropriate rigidities (flexural rigidity
and torsional rigidity), and makes the guide wire 1 rigid
for increased pushability and torque transmission
capability to give excellent insertion steerability.

The second wire 3 is made of any materials. For
example, the second wire 3 may be made of any of various
metal materials including stainless steels (all types of
SUS, e.g., SUS304, SUS303, SUS316, SUS316L, SUS316J1,
SUS316J1L, SUS405, SUS430, SUS434, SUS444, SUS429,
SUS430F, SUS302, etc.), piano wire, cobalt base alloys,
and pseudoelastic alloys. The second wire 3 may be made
of intermetallic materials.

Of these metal materials, the cobalt base alloys
have high elastic constants and appropriate elastic
limits when processed into wires. Therefore, the second
wire 3 made of a cobalt base alloy has a particularly
excellent torque transmission capability and is highly
unlikely to give rise to problems such as buckling. Any
cobalt base alloys containing Co as a constituent element
may be employed. However, cobalt base alloys containing
Co as a chief component (cobalt base alloys wherein the
content of Co has a largest wt% among the elements making
up the alloys) are preferable, and Co-Ni-Cr base alloys
are more preferable. The second wire 3 made of any of
alloys of the above compositions make the above
advantages more significant. Since the alloys of the
above compositions have plasticity when deformed at the
normal temperature, they can easily be deformed into
desired shapes when in use. The alloys of the above
compositions have high elastic constants, and can be
cold-formed with high elastic limits into a small-diameter
wire while sufficiently preventing buckling on
account of high elastic limits, the wire having
sufficient elasticity and rigidity for insertion into
desired body regions.

Preferable Co-Ni-Cr base alloys include alloys
containing 28 to 50 wt% of Co, 10 to 30 wt% of Ni, 10 to
30 wt% of Cr, and the balance being Fe and inevitable
impurities, and similar alloys having one of the elements
replaced with another element (substitute element). An
alloy containing a substitute element exhibits an
advantage inherent in the substitute element. For
example, if the second wire 3 contains at least one
selected from Ti, Nb, Ta, Be, and Mo as a substitute
element, then the mechanical strength of the second wire
3 can be increased. If the second wire 3 contains
elements (substitute elements) other than Co, Ni, Cr,
then the total content of those substitute elements is
preferably 30 wt% or less.

Part of Co, Ni, Cr may be replaced with another
element or elements. For example, part of Ni may be
replaced with Mn for better workability. Part of Cr may
be replaced with Mo and/or W for a higher elastic limit.
Of the Co-Ni-Cr base alloys, Co-Ni-Cr-Mo base alloys
containing Mo are particularly preferable.

If the second wire 3 is made of stainless steel,
then the guide wire 1 has better pushability and torque
transmission capability.

The first wire 2 and the second wire 3 are
preferably made of different alloys. The first wire 2 is
preferably made of a material having elastic constants
smaller than the second wire 3. With these materials,
the guide wire 1 has a distal end portion of excellent
flexibility and a proximal end of high rigidities
(flexural rigidity and torsional rigidity). As a result,
the guide wire 1 has excellent pushability and torque
transmission capability for better steerability, and the
distal end portion thereof gains better flexibility and
elasticity for increased ability to follow blood vessels
and increased safety.

According to one specific combination of the first
wire 2 and the second wire 3, the first wire 2 is
preferably made of a superelastic alloy (particularly, an
Ni-Ti base alloy) and the second wire 3 is preferably
made of a Co base alloy (particularly, a Co-Ni-Cr base
alloy) or stainless steel (an Fe-Cr-Ni base alloy) for
making the above advantages more significant. Another
reason for which the above combination is preferable is
that the materials of the first wire 2 and the second
wire 3 contain a common metal element (e.g., Ni). When
the first wire 2 and the second wire 3 are welded to each
other as described later, the bonding strength of the
joint 14 is increased by the common metal element. When
the guide wire 1 thus constructed is inspected in a
tensile test as described later, the joint 14 is
prevented from fracture. The guide wire 1 will thus be
highly reliable and safe in actual use in living bodies.

The second wire 3 has a generally constant outside
diameter, and includes a tapered portion 18 near its
distal end, i.e., near the joint 14, the tapered portion
18 having an outside diameter progressively smaller
toward the distal end. The tapered portion 18 causes the
physical properties, especially elasticity, from the
second wire 3 to the first wire 2 to change smoothly,
providing excellent pushability and torque transmission
performance across the joint 14 and increased kink
resistance. Alternatively, the second wire 3 may include
a portion having lower yield stresses or elastic
constants than the other portion thereof near the distal
end of the second wire 3. The distal end portion of the
second wire 3 is thus more flexible than the other
portion thereof. The first wire 2 is more flexible than
the distal end portion of the second wire 3. The guide
wire 1 which is thus made more flexible stepwise toward
the distal end thereof has excellent pushability, torque
transmission performance, and kink resistance.

The coil 4 includes a helically coiled filament
(thin filament), and is disposed around the distal end
portion of the first wire 2. In the illustrated
embodiment, the distal end portion of the first wire 2
extends substantially centrally through the coil 4 out of
contact with the inner surface of the coil 4. The joined
boundary area 14 is positioned more closely to the
proximal end of the guide wire 1 than the proximal end of
the coil 4.

In the illustrated embodiment, the coil 4 has
helically wound turns that are spaced apart in the
absence of external forces applied thereto. However, the
coil 4 may have helically wound turns that are held in
close contact in the absence of external forces applied
thereto.

The coil 4 is preferably made of a metal material
such as stainless steel, superelastic alloy, cobalt base
alloy, precious metal such as gold, platinum, tungsten,
or the like, or alloy containing precious metals, e.g.,
platinum-iridium alloy. If the coil 4 is made of an X-ray
impermeable material such as precious metal, then the
guide wire 1 is made radiopaque, and hence can be
inserted into a living body while the distal end thereof
is being positionally confirmed according to radioscopy.
The coil 4 may be made of different materials respective
at the distal and proximal end portions thereof. For
example, the distal end portion of the coil 4 may be made
of an X-ray impermeable material, and the proximal end
portion of the coil 4 may be made of a relatively X-ray
permeable material such as stainless steel. The overall
length of the coil 4 is preferably in the range from 5 to
500 mm.

The coil 4 has distal and proximal ends fixed to
the first wire 2 by respective fixing materials 11, 12.
The coil 4 also has an intermediate portion (closer to
the distal end) fixed to the first wire 2 by a fixing
material 13. The fixing materials 11, 12 and 13 include
a solder material (brazing material). Alternatively, the
fixing materials 11, 12 and 13 may include an adhesive.
The coil 4 may be fixed in place by welding, rather than
the fixing materials. The fixing material 12 preferably
have a round distal end surface for preventing blood
vessel walls from being damaged.

According to the present embodiment, since the
first wire 2 which is partly covered with the coil 4 has
a relatively small area of contact with a blood vessel
wall, the guide wire 1 undergoes reduced resistance to
its sliding movement, and hence has better steerability.

According to the present embodiment, the filament
of the coil 4 has a circular cross-sectional shape.
However, the filament of the coil 4 may have an
elliptical cross-sectional shape, a square cross-sectional
shape (particularly an elongate rectangular
cross-sectional shape), or the like.

The first wire 2 and the second wire 3 that
construct the guide wire 10 are preferably connected to
each other by welding. The joint (welded area) 14 of the
first wire 2 and the second wire 3 that are thus
connected to each other has such a high bonding strength
that torsional torques and pushing forces can reliably be
transmitted from the second wire 3 to the first wire 2.

As shown in Fig. 2, the joint 14 is in the form of a
layer. The term "layer" used herein covers not only a
visually perceptible layer, but also a conceptual layer
such as a distinctive content change, for example. The
laminar joint 14 extends in a direction substantially
perpendicular to the axis of the wire body 10. The joint
14 may be convex. The joint 14 is preferably convex
toward the axis of the wire body 10. Particularly, the
joint 14 may be convex toward the proximal end of the
wire body 10. Alternatively, the joint 14 may be convex
toward the distal end of the wire body 10. The joint 14
may be convex toward one wire formed of a material having
an elastic constant greater than a material of the other
wire. Alternatively, the joint 14 may be convex toward
one wire formed of a material having an elastic constant
lower than a material of the other wire. The curved
shape of the joint 14 is preferably substantially
symmetric with respect to the central axis of the wire
body 10. Specifically, the curved shape of the joint 14
is preferably shaped as a body of rotation about the
central axis of the wire body 10. The body of rotation
may be of a dish shape, a spherical shape, a parabolic
shape, or a shape similar to one of those shapes. The
thickness of the laminar joint 14 is preferably in the
range from 0.001 to 100 µm, more preferably in the range
from 0.1 to 15 µm, or much more preferably in the range
from 0.3 to 2 µm. The thickness of the laminar joint 14
is preferably constant, though it may be locally
increased. The laminar joint 14 having the above
thickness is effective to provide a higher bonding
strength.

In Fig. 2, the boundary surfaces between the
laminar joint 14 and the materials of the first and
second wires 2, 3 are clearly visible for an easier
understanding. However, no such clear boundary surfaces
may be present between the laminar joint 14 and the
materials of the first and second wires 2, 3.

The joint 14 which is produced by welding includes
therein the components (metal elements) of the metal
material of the first wire 2 and the components (metal
elements) of the metal material of the second wire 3.
The material composition may preferably change gradually
from the first wire 2 through the joint 14 to the second
wire 3. The material composition may preferably change
continuously from the first wire 2 through the joint 14
to the second wire 3. The joint 14 may have a portion in
which at least one of the components of the material of
the first wire 2 is reduced toward the proximal end, i.e.,
the second wire 3. The joint 14 may have a portion in
which at least one of the components of the material of
the second wire 3 is reduced toward the distal end, i.e.,
the first wire 2. More preferably, in the joint 14, at
least one of the components of the material of the first
wire 2 is reduced toward the proximal end, i.e., the
second wire 3, and at least one of the components of the
material of the second wire 3 is reduced toward the
distal end, i.e., the first wire 2.

Specific examples will be described below. If the
first wire 2 is made of an Ni-Ti base alloy and the
second wire 3 is made of stainless steel (Fe-Cr-Ni base
alloy), then in the joint 14, Fe and Cr have a decreasing
tendency from the second wire 3 toward the first wire 2,
and Ni and Ti have a decreasing tendency from the first
wire 2 toward the second wire 3.

Fig. 3 is a graph showing the results of an Auger
electron spectroscopic analysis of the composition along
the longitudinal axis of a wire body which was
constructed by welding, according to butt resistance
welding, a first wire 2 made of Ni-Ti alloy containing
55.91 wt% of Ni and the balance being Ti and inevitable
impurities including C, O, etc., and a second wire 3 made
of a stainless steel (SUS302) containing 18.19 wt% of Cr,
8.03 wt% of Ni, and the balance being Fe and inevitable
impurities including Mn etc.

As shown in Fig. 3, the concentrations of Ni and Ti,
which are components of the first wire 2, are
substantially constant in the first wire 2 and decrease
in the joint 14 toward the second wire 3. In, the second
wire 3, the concentration of Ni is substantially constant,
and the concentration of Ti is substantially nil. In the
second wire 3, the concentrations of Fe and Cr, which are
components of the second wire 3, are substantially
constant. In the first wire 2, the concentrations of Fe
and Cr are substantially nil. In the joint 14, the
concentrations of Fe and Cr increase toward the second
wire 3.

As shown in Fig. 3, the weld joint 14 may have at
least a portion such that at least one component of the
material of the first wire 2 decreases toward the
proximal end. The weld joint 14 may have at least a
portion such that at least one component of the material
of the second wire 3 decreases toward the distal end. For
example one component of the material of the first wire 2
may be Ti, and one component of the material of the
second wire 3 may be Fe.

More specifically, in the joint 14, the
concentrations of Ni and Ti near the first wire 2
gradually decrease toward the second wire 3, abruptly
drop across a certain region, and gradually decrease near
the second wire 3. That is, in a region including the
joint 14, at least one of the components of the material
of the first wire 2 decreases at least two different
concentration gradients toward the second wire 3. The
concentrations of Ni and Ti in the joint 14 have a first
concentration gradient gradually decreasing near the
first wire 2 toward the proximal end, a second
concentration gradient gradually decreasing near the
second wire 3 toward the proximal end, and a third
concentration gradient positioned intermediate between
the first and second concentration gradients and steeper
than the first and second concentration gradients. In
the joint 14, the concentration of Fe near the second
wire 3 gradually decreases toward the distal end,
abruptly drops across a certain region, and gradually
decreases near the first wire 2. That is, in a region
including the joint 14, at least one of the components of
the material of the second wire 3 decreases at least two
different concentration gradients toward the first wire 2.
The concentration of Fe in the joint 14 has a first
concentration gradient gradually decreasing near the
second wire 3 toward the distal end, a second
concentration gradient gradually decreasing near the
first wire 2 toward the distal end, and a third
concentration gradient positioned intermediate between
the first and second concentration gradients and steeper
than the first and second concentration gradients.

The first and second concentration gradients and
the third concentration gradient may be analyzed as
follows: When the first and second wires 2 and 3 are
welded to each other, the components typified by Ni and
Ti of the first wire 2 and Fe, Cr, and Ni of the second
wire 3 are mixed with each other. When Fe and Ti are
mixed with each other, they usually produce a brittle
intermetallic compound. According to the present
invention, the area where Fe and Ti are mixed with each
other is highly thinned to make the intermetallic
compound hardly brittle. The area where Fe and Ti are
mixed with each other corresponds to the third
concentration gradient. At the first and second
concentration gradients on both sides of the third
concentration gradient, the components Fe and Ti are
considered to be gradually reduced or increased by way of
diffusion. Since the first and second concentration
gradients are present continuously on both sides of the
third concentration gradient, the continuity of the
atomic arrangement is maintained, and abrupt property
changes are lessened, making the intermetallic compound
hardly brittle. As the first and second concentration
gradients, which are more gradual than the third
concentration gradient, are present on both sides of the
third concentration gradient, the joint 14 keeps a strong
bonding strength against not only tensile stresses, but
also bending and torsional stresses.

The elements may be analyzed not only by the Auger
electron spectroscopic analysis, but also by any of
various analyses including an X-ray photoelectron
spectroscopic analysis (XPS), an electron probe X-ray
microanalysis (EPMA), a fluoroscopic X-ray analysis, etc.

The change in the composition (components) in the
joint 14 and wire regions on both sides thereof provide a
higher bonding strength.

The first wire 2 and the second wire 3 may be
welded to each other by any welding processes, e.g.,
friction welding, laser-beam spot welding, butt
resistance welding such as butt seam welding, etc. Of
these welding processes, butt resistance welding is
preferable for its ability to achieve a high bonding
strength relatively simply. When the first wire 2 and
the second wire 3 are welded to each other by butt
resistance welding, the following conditions are
preferable which depend upon the materials and the
outside diameters of the wires to be welded. The wires
may be pressurized under a pressure ranging from 30 to
400 kgf/mm2. If the pressure is lower than 30 kgf/mm2,
then a spark failure will occur. If the pressure is
higher than 400 kgf/mm2, then the welding machine will be
possible to be broken. More preferably, the wires may be
pressurized under a pressure ranging from 50 to 200
kgf/mm2. The value of a current to be passed through the
wires is preferably in the range from 40 to 1000 A. If
the current value is lower than 40 A, then the bonding
strength will be weak, and if the current value is higher
than 1000 A, then the bonding strength will be greatly
lowered. More preferably, the value of the current may
be in the range from 60 to 700 A. The current may be
passed preferably for a period of time ranging from 5 to
100 ms. If the period of time for which the current is
passed is shorter than 5 ms, then no desired current
value will be achieved, and if the period of time for
which the current is passed is longer than 100 ms, then
the bonding strength will not be increased. More
preferably, the current may be passed for a period of
time ranging from 10 to 60 ms.

The joint 14 may be of a planar shape. The joint 14
is preferably of a curved shape as shown in FIGS. 1 and 2.
Particularly, the joint 14 may be convex toward the
proximal end of the wire body 10. Alternatively, the
joint 14 may be convex toward the distal end of the wire
body 10. The curved shape of the joint 14 is preferably
substantially symmetric with respect to the central axis
of the wire body 10. Specifically, the curved shape of
the joint 14 is preferably shaped as a body of rotation
about the central axis of the wire body 10. The body of
rotation may be of a dish shape, a spherical shape, a
parabolic shape, or a shape similar to one of those
shapes.

The joint 14 thus shaped offers the following
advantages. Since the joint 14 is of a curved shape, it
provides a greater joint area than if the joint 14 were
of a planar shape, and provides a high bonding strength
since it distributes stresses when bent. Because the
curved shape of the joint 14 is symmetric with respect to
the central axis of the wire body 10, when the wire body
10 is twisted, the joint 14 can transmit the torque
uniformly (without deviations) from the second wire 3 to
the first wire 2. These advantages contribute to
increased steerability.

The outside diameter of the wire body 10 at the
joint 14 is greater than the outside diameter of a
proximal side of the joint 14. More preferably, as shown
in Fig. 2, the outside diameter of the wire body 10 at
the joint 14 is greater than the outside diameters of
distal and proximal sides of the joint 14. A certain
region of the wire body 10, which includes the joint 14,
has a portion 17 projecting (raised) radially outwardly.
The portion 17 gives a greater joint area to the joint 14
for an increased bonding strength, which allows torsional
torques and pushing forces to be transmitted from the
second wire 3 to the first wire 2.

The portion 17 also makes it possible to easily
visually recognize an area where the joint 14 is present
according to radioscopy, for example. As a result, the
manner in which the guide wire 1 or the catheter combined
therewith travels through a blood vessel can easily and
reliably be grasped by confirming the radioscopic image,
resulting in a reduction in the period of time required
to operate the patient and an increase in the safety of
the guide wire 1.

The height of the portion 17 is preferably in the
range from 1 µm to 0.4 mm, and more preferably from 5 to
50 µm. If the height of the portion 17 is less than the
lower limit, the advantages of the portion 17 may not
possibly be offered depending on the materials of the
first wire 2 and the second wire 3. If the height of the
portion 17 exceeds the upper limit, the second wire 3 may
be difficult to have desired properties. Since the
inside diameter of a lumen to be inserted into the
balloon catheter is determined, the outside diameter of
the second wire 3 closer to the distal end has to be
reduced compared with the height of the portion 17.

The portion 17 is formed, for example, as follows.
The proximal end of the first wire 2 and the distal end
of the second wire 3 are held under pressure in contact
with each other while a certain voltage is being applied
thereto by a butt welding machine, for example. When the
first and second wires 2 and 3 are held under pressure in
contact with each other, a molten layer is formed in the
contacting region. The molten layer is cooled and
solidified into the joint 14, firmly joining the first
wire 2 and the second wire 3. When the first and second
wires 2 and 3 are welded together, a raised portion
having a large outside diameter is formed in a certain
region including the joint 14, e.g., a region extending
over 0.1 to 5 mm across the joint 14. The raised portion
is appropriately removed (deleted) to shape, thus forming
the portion 17. The portion 17 may have a substantially
smooth outer circumferential surface. The raised portion
may be removed by grinding, polishing, or chemical
processing such as etching or the like.

A tube-like member may be disposed about the region
including the joint 14. The region has a smaller diameter
portion. The diameter of the region is preferably the
same as an inner diameter of the tube-like member. The
tube-like member includes a cylindrical member, a mesh-like
member and a coil-like member.

The wire body 10 has the following mechanical
characteristics. Figs. 4, 5(a), and 5(b) are diagrams
showing the relationship between tensile loads and
elongations in a tensile test conducted on the wire body
10. The mechanical characteristics of the wire body 10
will be described in detail below with reference to Figs.
4, 5 (a), and 5(b).

A tensile test is conducted on a region of the wire
body 10. The wire body 10 has a certain length including
the joint 14, e.g., a region having a length ranging from
20 to 60 mm across the joint 14. The tensile load and
elongation diagram shown in Fig. 4 has an elastic section
A, a yield section B, and a straight section C. The
elastic section A extends substantially straight upwardly
to the right. The yield section B extends substantially
horizontally (or upwardly to the right) from the elastic
section A. The straight section C extends substantially
straight upwardly to the right from the yield section B.
The wire body 10 is fractured near the terminal end of
the straight section C under a load higher than at the
terminal end of the yield section B. The wire body 10 is
fractured at a position other than the joint 14, i.e.,
somewhere at the first wire 2 or somewhere at the second
wire 3.

When the wire body 10 starts being pulled, the
substantially straight elastic section A first appears in
the tensile load and elongation diagram. As a more load
is applied to the wire body 10 from the elastic section A,
the yield section B having a less gradient than the
elastic section A appears in the tensile load and
elongation diagram.

Since the first wire 2 is made of a material having
smaller elastic constants than the second wire 3, the
elastic section A is considered to be developed by the
physical properties of the material of the first wire 2.
If the first wire 2 itself exhibits a substantially
horizontal tensile load and elongation curve, then the
yield section B is represented by a substantially
straight and horizontal (flat) curve (see Fig. 4). The
joint 14 is not fractured at the terminal end (the right
end in Fig. 4) of the yield section B. That is, the
layer itself of the joint 14 (inside the layer), the
boundary between the layer and the first wire 2, and the
boundary between the layer and the second wire 3 are not
fractured.

Then, the substantially straight section C
extending upwardly to the right appears beyond the yield
section B. The straight section C is considered to be
developed by the physical properties of the materials of
both the first and second wires 2 and 3. The joint 14
has fracture strength beyond the yield section B.
Therefore, even when the first wire 2, which is more
flexible than the second wire 3, is pulled, bent, or
twisted closely at the joint 14 under forces
corresponding to the terminal end of the yield section B,
the joint 14 remains joined. Accordingly, the guide wire
1 is highly reliable and safe.

As a more load is applied to the wire body 10, the
wire body 10 is eventually fractured at a fracture point
D in the straight section C. The fracture is represented
by a curve extending vertically downwardly from the
fracture point D in the tensile load and elongation
diagram. The terminal end of the straight section C is
the fracture point D. An inspection of the fracture
point D at an enlarged scale indicates that the tensile
load and elongation curve has a curved section E where
the tensile load and elongation curve reaches a peak and
then falls downwardly (see an enlarged area in Fig. 4).

The curved section E appears when the distal end of
the second wire 3 causes necking (a constriction due to a
reduction in the outside diameter, also referred to as
neck-down) as the wire body 10 approaches the fracture
point D. As the degree of necking is smaller, the radius
of curvature of the curved section E is smaller,
resulting in a sharper peak. Such necking means that the
wire material is tougher, preventing the guide wire from
causing abrupt fracture even when subjected to excessive
stresses.

The wire body 10 is often fractured generally at
the position where it has suffered necking. The fact
that the distal end of the second wire 3, where necking
has occurred, is fractured means that the layer itself of
the joint 14 (inside the layer), the boundary between the
layer and the first wire 2, and the boundary between the
layer and the second wire 3 are not fractured, and that
the joint 14 has a higher fracture strength than the
distal end of the second wire 3. As a result, the guide
wire 1 is highly reliable and safe.

The fracture strength of the wire body 10 is
preferably 4 kgf (445 MPa) or higher, or more preferably
5 kgf (556 MPa) or higher, or much more preferably 8 kgf
(890 MPa) or higher.

Figs. 5(a) and 5(b) show other patterns of tensile
load and elongation diagrams. According to the tensile
load and elongation diagram shown in Fig. 5(a), the
elastic section A and the yield section B are essentially
the same as those shown in Fig. 4, but the straight
section C has a greater gradient (rises more steeply)
than the straight section C shown in Fig. 4. Such a
tendency appears if the second wire 3 is made of a
material having greater elastic constants (higher
rigidity) or the second wire 3 has a greater outside
diameter.

According to the tensile load and elongation
diagram shown in Fig. 5(b), the elastic section A and the
straight section C are essentially the same as those
shown in Fig. 4, but the yield section B extends upwardly
to the right and is substantially straight. The gradient
of the yield section B is smaller than the gradient of
the elastic section A and smaller than the gradient of
the straight section C. For example, this tendency is
exhibited if the first wire 2 itself is made of a
pseudoelastic material represented by a tensile load and
elongation curve (stress and strain curve) that extends
upwardly to the right even after the yield point. The
tendency is also exhibited if the first wire 2 is of a
tapered shape having an outside diameter progressively
reduced in the vicinity of the joint 14 toward the distal
end. In addition, a load beyond the elastic section A is
applied to the tapered portion of the first wire 2. Even
if the first wire 2 is made of a material exhibiting a
flat yield section, the shape of the first wire 2 affects
the tensile load and elongation curve to cause the yield
section B to have a gradient.

If the tensile rate in a tensile test on the wire
body 10 is relatively low, e.g., if the tensile rate is
about 0.5 mm/min., then the yield section B of the
tensile load and elongation curve tends to be horizontal
or extend upwardly to the right at a relatively small
gradient. If the tensile rate is relatively high, e.g.,
if the tensile rate is about 5 mm/min., then the yield
section B of the tensile load and elongation curve tends
to extend upwardly to the right at a relatively large
gradient.

A specific example of the present invention will be
described below.

The tensile test is conducted as follows on a
region of the wire body 10 including the joint 14
according to the present invention. An Ni-Ti alloy wire
having an outside diameter of 0.335 mm (first wire 2) and
a stainless steel (SUS302) wire having an outside
diameter of 0.335 mm (second wire 3) were welded to each
other by butt resistance welding. Further, a raised
portion (burr) formed on the joint was mechanically
polished off to provide a substantially uniform outside
diameter. The test specimen thus formed was fixed to the
chucks of a tensile tester such that the Ni-Ti alloy wire
was positioned upwardly, the stainless steel wire was
positioned downwardly, with the joint positioned
centrally. The distance between the chucks was 40 mm,
and the length of each of the Ni-Ti alloy wire and the
stainless steel wire was 20 mm. The tensile rate was 0.5
mm/min. Under the above conditions, the test specimen
was pulled until it was fractured. Fig. 6 shows a
tensile load and elongation diagram of the tensile test.

In Fig. 6, a region of the joint 14 of the test
specimen exhibits a substantially straight elastic
section extending upwardly to the right. As a more load
is applied to the test specimen, a substantially
horizontal yield section was developed under a load in
excess of 4 kgf (a stress of 445 MPa). Then, a straight
section extending upwardly to the right appeared. The
test specimen caused necking when it was elongated 6%
under a load of 8 kgf (a stress of 890 MPa), after which
the test specimen was fractured. Actually, the test
specimen was fractured at a position on the stainless
steel wire near the joint 14, but not at the joint 14.
This indicates that the joint 14 has higher fracture
strength than the distal end of the second wire 3 in the
guide wire of the present invention.

The tensile load and elongation diagrams shown in
Figs. 4 and 5(a), 5(b) are schematically illustrated only.
The present invention covers various changes or
modifications in those tensile load and elongation
diagrams, such as slight curves in straight sections and
round curves in bent sections. The tensile load and
elongation curves according to the present invention are
not limited to the patterns illustrated in Figs. 4, 5(a),
and 5(b).

As shown in Fig. 1, the wire body 10 has the
covering layer 5 covering all or part of the outer
circumferential surface (outer surface) thereof. The
covering layer 5 is omitted from illustration in Fig. 2.
The covering layer 5 may be formed for various purposes.
According to one purpose, the covering layer 5 serves to
reduce friction (sliding resistance) and improve the
slidability of the guide wire 1 for increased
steerability thereof.

The covering layer 5 is preferably provided in
covering relation to the outer circumference of at least
the joint 14. As described above, since the outside
diameter of the wire body 10 has a change (a step) in the
vicinity of the joint 14, the covering layer 5 cancels or
reduces the outside diameter change, making the outside
diameter of the guide wire 1 substantially uniform in the
vicinity of the joint 14. As a result, the steerability
of the guide wire 1 for longitudinal movement thereof is
improved.

To serve the above purpose, the covering layer 5 is
preferably made of a material capable of reducing
friction. If the covering layer 5 is made of such a
material, then the frictional resistance (sliding
resistance) thereof with respect to the inner wall of the
catheter used in combination with the guide wire 1 is
reduced for increased slidability, thus improving the
steerability of the guide wire 1 in the catheter. Since
the sliding resistance of the guide wire 1 is lowered,
when the guide wire 1 is moved and/or rotated in the
catheter, the guide wire 1 is more reliably prevented
from kinking or twisting especially in the vicinity of
the joint 14.

Of the above materials, fluorine-based resin or its
composite material is capable of more effectively
reducing frictional resistance (sliding resistance)
between the guide wire 1 and the inner wall of the
catheter for increased slidability and improved
steerability of the guide wire 1 in the catheter. When
the guide wire 1 is moved and/or rotated in the catheter,
the guide wire 1 is reliably prevented from kinking or
twisting especially in the vicinity of the joint 14.

If fluorine-based resin or its composite material
is used, then it is heated and applied as the covering
layer 5 to the wire body 10 usually by baking or spraying.
The wire body 10 and the covering layer 5 thus applied
thereto adhere closely to each other.

If silicone resin or its composite material is used,
then it can be applied as the covering layer 5 to the
wire body 10 without being heated. The covering layer 5
thus formed is reliably and firmly held in close adhesion
to the wire body 10. Specifically, if the covering layer
5 is made of silicone resin or its composite material,
the material may be a reaction-curable material. The
covering layer 5 may be formed at the room temperature.
Since the covering layer 5 is formed at the room
temperature, the wire body 10 can easily be coated with
the covering layer 5. Further, the guide wire 3 can be
steered while the bonding strength of the joint 14
between the first wire 2 and the second wire 3 is being
kept at a sufficient level.

Other preferable materials capable of reducing
friction may be hydrophilic materials and hydrophobic
materials. Of these materials, hydrophilic materials are
preferable.

These hydrophilic materials exhibit a lubricating
capability when wetted (absorbing water) and reducing the
frictional resistance (sliding resistance) between the
guide wire 1 and the inner wall of the catheter that is
used in combination therewith. The slidability of the
guide wire 1 is thus increased to improve the
steerability of the guide wire 1 in the catheter.

The covering layer 5 may be provided for the
purpose of increasing safety at the time the guide wire 1
is inserted into a blood vessel. To serve this purpose,
the covering layer 5 is preferably made of a flexible
material (soft material).

Flexible materials that can be used include, for
example, polyolefin such as polyethylene or polypropylene,
polyvinyl chloride, polyester (PET, PBT, etc.), polyamide,
polyimide, polyurethane, polystyrene, silicone resin,
thermoplastic elastomer such as polyurethane elastomer,
polyester elastomer, polyamide elastomer, or the like,
various rubber materials including latex rubber, silicone
runner, etc., or composite materials in the form of a
combination of two or more of the above materials.

If the covering layer 5 is made of thermoplastic
elastomer such as polyurethane elastomer or the like or
any of the rubber materials, then since the distal end of
the guide wire 1 is made more flexible, it reliably
prevents damage to the blood vessel wall when inserted
into a blood vessel, and is highly safe in use.

The covering layer 5 may include a laminated
assembly of two or more layers, and may have different
material compositions depending on the location on the
wire body 10. For example, the covering layer 5 may be
made of a material in a region covering the joint 14 and
a different material in another region. The covering
layer 5 on the distal end of the guide wire 1, e.g., the
region closer to the distal end than the tapered portion
16, may be made of a soft material, as described above,
for increased safety, and the covering layer 5 on the
other region may be made of a friction-reducing material,
as described above, for increased steerability.

The thickness of the covering layer 5 is not
limited, and may be selected in view of the purpose and
the material of the covering layer 5, and the method by
which the covering layer 5 is formed. Usually, the
thickness (average) of the covering layer 5 is preferably
in the range from 1 to 30 µm, and more preferably from 2
to 15 µm. If the covering layer 5 is too thin, then the
purpose of the covering layer 5 may not sufficiently be
met, and the covering layer 5 may possibly be peeled off.
If the covering layer 5 is too thick, then it may
possibly adversely affect the physical properties of the
wire body 10, and the covering layer 5 may possibly be
peeled off.

According to the present invention, the outer
circumferential surface of the wire body 10 may be
treated by way of chemical treatment, heat treatment, or
the like for increasing the adhesion of the covering
layer 5. Alternatively, an intermediate layer capable of
increasing the adhesion of the covering layer 5 may be
provided on the outer circumferential surface of the wire
body 10.

Figs. 7 and 8 are illustrative of an example in
which the guide wire 1 according to the present invention
is used in PTCA.

Figs. 7 and 8 show an aortic arch 40, a right
coronary artery 50, a right coronary artery opening 60,
and a blood vessel constriction (lesion) 70. A guiding
catheter 30 serves to guide the guide wire 1 from a
femoral artery reliably into the right coronary artery 50.
A balloon catheter 20 for dilating the blood vessel
constriction 70 has an dilatable/contractible balloon 201
on its distal end portion. The following operation is
performed according to radioscopy.

As shown in Fig. 7, the distal end of the guide
wire 1 is projected from the distal end of the guiding
catheter 30, and inserted from the right coronary artery
opening 60 into the right coronary artery 50. The guide
wire 1 is further moved on in the right coronary artery
50 and then stopped when the distal end of the guide wire
1 reaches a position beyond the blood vessel constriction
70. A passage for the balloon catheter 20 is now formed.
At this time, the joint 14 of the guide wire 1 is
positioned in a descending aorta of the aortic arch 40.

Then, as shown in Fig. 8, the distal end of the
balloon catheter 20, which is inserted from the proximal
end of the guide wire 1, is projected from the guiding
catheter 30, and is further moved along the guide wire 1
so as to be inserted from the right coronary artery
opening 60 into the right coronary artery 50. The distal
end of the balloon catheter 20 is then stopped when the
balloon 201 reaches the blood vessel constriction 70.

Then, a balloon-dilating fluid is poured into the
balloon catheter 20 from the distal end thereof to dilate
the balloon 201, thereby dilating the blood vessel
constriction 70. A deposit such as of cholesterol on the
blood vessel wall in the blood vessel constriction 70 is
physically dilated, thereby eliminating the blood flow
blockage.

The guide wire according to the present invention
has been described above with respect to the illustrated
embodiment. However, the present invention is not
limited to the illustrated embodiment. The components of
the guide wire according to the present invention may be
replaced with other components or members that are
capable of the same functions, and other components or
members may be added to the guide wire.

The guide wire according to the present invention
is not limited to the use in PTCA.

The principles of the present invention have been
described as being applied to a guide wire. However, the
principles of the present invention are also applicable
to other uses than the guide wire, e.g., an
interventional device such as a catheter having a
component made up of a distal end member and a proximal
end member that are welded to each other. Other
interventional devices include, by way of example and not
limitation, baskets, and retrieval devices.

Although certain preferred embodiments of the
present invention has been shown and described in detail,
it should be understood that various changes and
modifications may be made therein without departing from
the scope of the appended claims.

A guide wire (1) has a wire body (10) having a
first wire (2) disposed at a distal end thereof and a
second wire (3) joined to a proximal end of the first
wire. The first wire (2) and the second wire (3) are
preferably joined to each other by welding, providing a
layer joint (14) therebetween. The joint (14) is of a
curved shape, particularly, a convex curved shape that is
convex toward the proximal end of the wire body (10). In
the joint (14), at least one component (e.g., Ti) of the
material of the first wire (2) decreases toward the
proximal end, and at least one component (e.g., Fe) of
the material of the second wire (3) decreases toward the
distal end. When a tensile test is conducted on a region
of the wire body (10) including the joint (14), the
region of the wire body (10) has, in a tensile load and
elongation diagram, an elastic section extending
substantially straight upwardly to the right, a yield
section extending substantially horizontally or upwardly
to the right from the elastic section, and a
substantially straight section extending upwardly to the
right from the yield section. The region of the wire
body (10) has such characteristics that the region is
fracturable near a terminal end of the straight section
at a fracture position on other than the joint (14).

Claims (20)

A guide wire (1) comprising a wire body (10) having
a first wire (2) disposed at a distal end thereof and a
second wire (3) joined to a proximal end of said first
wire (2) through a weld joint (14) and made of a material
different from the material of said first wire (2).

A guide wire (1) according to claim 1, wherein the
material of said second wire (3) has an elastic constant
greater than the material of said first wire (2).

A guide wire (1) according to claim 1 or 2, wherein
in said joint (14) at least one component of the material
of said first wire (2) decreases toward the proximal end,
and/or at least one component of the material of said
second wire (3) decreases toward the distal end.

A guide wire (1) according to any one of the
preceding claims, wherein the materials of said first
wire (2) and said second wire (3) contain a common metal
element.

A guide wire (1) according to any one of the
preceding claims, wherein said first wire (2) is made of
a pseudoelastic material.

A guide wire (1) according to claim 6, wherein said
pseudoelastic material is a superelastic alloy.

A guide wire (1) according to claim 6, wherein said
superelastic alloy is a Ni-Ti base alloy.

A guide wire (1) according to any one of the
preceding claims, wherein said second wire (3) is made of
stainless steel or a Co base alloy.

A guide wire (1) according to any one of the
preceding claims, wherein said joint (14) has a curved
shape.

A guide wire (1) according to claim 9, wherein said
joint (14) has a curved shape which is symmetric with
respect to the central axis of said wire body (10).

A guide wire (1) according to claim 9 or 10, wherein
said joint (14) is convex toward the proximal end of said
wire body (10).

A guide wire (1) according to claim 9 or 10, wherein
said joint (14) is convex toward the distal end of said
wire body (10).

A guide wire (1) according to any one of the
preceding claims, wherein said joint (14) comprises a
layer.

A guide wire (1) according to claim 13, wherein said
joint (14) has a thickness ranging from 0.001 to 100 µm.

A guide wire (1) according to any one of the
preceding claims, wherein said wire body (10) has an
outside diameter at said joint (14) which is greater than
the outside diameter of a region of said wire body (10)
on a proximal side of said joint (14).

A guide wire (1) according to any one of the
preceding claims, wherein
when a tensile test is conducted on a region of said
wire body (10) including said joint (14), said region of
the wire body (10) has, in a tensile load and elongation
diagram, an elastic section (A) extending substantially
straight upwardly to the right and a yield section (B)
extending substantially horizontally or upwardly to the
right from said elastic section (A), and
said region of said wire body (10) has such
characteristics that the region is fracturable at a
fracture position under a load higher than a terminal end
of said yield section (B), said fracture position being
on other than said joint (14).

A guide wire (1) according to claim 16, wherein
said region of the wire body (10) has, in said
tensile load and elongation diagram, a substantially
straight section (C) extending upwardly to the right from
said yield section (B) and the region is fracturable near
a terminal end (D) of said straight section (C), and
said joint (14) has a higher fracture strength than
the distal end of said second wire (3).

A guide wire (1) according to claim 16 or 17,
wherein said tensile load and elongation diagram includes
a tensile load and elongation curve (E) which is curved
downwardly due to necking of the guide wire (1) when the
guide wire (1) is going to be fractured.

A guide wire (1) according to any one of claims 16
to 18, wherein said wire body (10) has a fracture
strength of at least 4 kgf (445 MPa).

A guide wire (1) comprising a wire body (10) having
a first wire (2) disposed at a distal end thereof and a
second wire (3) joined to a proximal end of said first
wire (2) through a joint (14) and made of a material
different from the material of said first wire (2),
wherein said joint (14) has a curved shape which is
symmetric with respect to the central axis of said wire
body (10).